Helically threaded intermeshing rotors



June 23, 1964 .1. E. WHITFIELD 3,138,110

HELICALLY THREADED INTERMEISHING ROTORS Filed June 5, 1962 8 Sheets-Sheet 2 INVENTOR. 61 Joseph E.Whhfield ATTORNEYS June 1964 J. E. WHITFIELD 3,138,110

HELICALLY THREADED INTERMESHING ROTORS Filed June 5, 1962 8 Sheets-Sheet 3 INVENTOR.

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June 23, 1964 J. E. WHITFIELD 3,138,110 HELICALLY THREADED INTERMEZSHING ROTORS Filed June 5, 1962 8 Sheets-Sheet 7 peer Q12 0 F RM Fl 5 a2 70 4/ INVENTOR.

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HELICALLY THREADED INTERMESHING ROTORS Filed June 5, 1962 8 Sheets-Sheet 8 FIG. 58 INVENTOR.

Joseph E.Whirfleld BY eaflnman, mra/WIAM ATTO/P/VKYS' United States Patent 3,138,11d HELTCALLY THREADED INTERMESHEJG ROTORS Joseph E. Whitfield, Box 325, York, Pa. Filed June 5, 1962, Ser. No. 200,242 13 Claims. (Cl. 103-128) This invention relates generally to compressors, blowers, liquid pumps, meters, air motors, liquid motors and similar devices in which interengaging rotary members are provided with intermeshing helical threads, and is directed particularly to the rotary members of such devices.

Screw type devices of this general nature have two or more helically threaded members rotatably supported with their axes substantially parallel and with their complementary threads interrneshing to form a working seal between the rotors. A housing encloses the rotary members and the chambers of said housing form a working seal with the perimetric tips of the rotor threads. Thus, in operation, the fluid being pumped from the suction end of the housing to the discharge end is confined in individual pockets, the fluid being separated into individual slugs. As the rotors rotate the pockets develop continuously at the suction end and fill with fluid as they increase in size because of the vacuum thus created. The pockets progress axially along the rotors and diminish progressively in size at the discharge end until they are reduced to zero or run out, thus expelling the fluid being pumped through the discharge port.

The threads must be complementary to form satisfactory seals and spaces and to permit rotation of the members. Thus the rotors are dissimilar in cross section and one has right-hand threads while the other has lefthand threads.

While more than two rotors can be used without depart ing from the spirit of this invention, only two will be shown and described herein for reasons of simplicity. The threads on one rotor lie wholly, or almost wholly, outside its pitch circle and, as this rotor absorbs almost all the input power, it is termed the main rotor. The threads on the mating rotor lie wholly, or almost wholly, within its pitch circle and, as this rotor forms a gate across the path of the main rotor threads, it is termed the gate rotor. If a gate rotor or some other device were not provided across the path of the main rotor threads, the fluid being pumped would simply revolve with the main rotor and no pumping effect would be produced.

The main rotor is sometimes termed the male rotor and the gate rotor is sometimes termed the female rotor. However, in this disclosure, the terms main and gate rotors will be used because they are more accurately descriptive of the members to which they are applied.

As the rotors are rotated the threads on the main rotor, in effect, act as a continuous series of pistons which progress endwise through the troughs formed by the gate rotor threads, and form a continuous series of compression spaces, or pockets, which convey the fluid from the suction end to the discharge end of the housing in the form of separate, distinct slugs. The opening at the inlet end of the housing is called the suction port and the opening at the outlet end of the housing is termed the discharge port.

Axial flow devices of the general type here involved are old and well known in the art. However, practically all previous devices have rotors that are of the same shape, or cross section, throughout their length, and are usually reversible so far as the rotors are concerned. This disclosure describes a device in which the rotors change shape near the discharge end and which operates to best advantage in one direction only. When rotors are of the same shape throughout their length the shape must be Patented June 23, 1964 air:

a compromise between two sets of conditions as the conditions of lluid handling are completely different atthe suction and discharge ends. By providing rotors that are not the same shape at the suction and discharge ends the correct shape can be provided for each individual end and the device becomes more efiicient.

For example, to provide proper sealing through the compresison area the rotors will be of the generated form and will produce sealed pockets at the suction end, thus creating partial vacuums for short periods of each revolution. These partial vacuums are not objectionable as the vacuum produced cannot be of high intensity. However, it this same type of rotor is continued for the full rotor length, such rotors will also create sealed pockets at the discharge end but these pockets will be compression pockets. Since all fluid in these pockets must be forced through the normal running clearances, the pressure may be extremely high. This excess pressure creates high temperature, noise and excess bearing loads all of which tend to decrease efficiency. It is usually impossible to pump liquids with such a device as liquids are considered non-compressible.

Many attempts have been made to eliminate these closed pockets by changing the shape of the rotors, by

cutting by-pass grooves in the ends of the rotors, or in the housing or by removing that part of the housing end wall that creates the closed pocket. However, all these expedients are subject "to serious objections because they create leakage paths or loss on volume. For example, in Nilsson Patent No. 2,622,787 wherein rotors having threads with arcuate profiles are used, the thread of the I main rotor fits the trough of the gate rotor only when the threads are fully in mesh, and leakage paths are formed from the discharge end to the suction end of the rotors as explained in detail later. In Whitfield Patent No. 2,287,716 grooves are cut in the discharge ends of the rotors to prevent over compression, but the compressed iiuid in these grooves is carried around to the suction side and thus represents a loss. If part of the discharge end wall normally used is cut away to prevent formation of closed pockets, an opening will be produced which will eliminate the closed pockets, since they cannot be formed without the end wall, but this opening will also provide a direct leakage path from the discharge side to the suction side of the device during certain periods of each revolution.

To produce a more ideal blower of this type it is necessary that the sealing lines remain unbroken during the period of compression and that no by-pass openings occur to directly connect the suction side to the discharge side of the device during the discharge period.

The rotors shown in Whitfield Patent No. 2,922,377 have the proper operating characteristics but are difficult to construct, and the cones reduce the capacity. On

the other hand, the rotors disclosed herein not only have all the advantages of the aforementioned Patent No. 2,922,377, but also are easier to construct, have greater capacity, and have improved sealing lines in the high pressure area due to the elimination of sharp sealing edges as hereinafter described.

The number of threads on each rotor of a screw type compressor or similar device is generally a matter of choice and depends upon the speed, pressure ratio, volume and other considerations. For high speed and high pressure the number of threads used is usually greater than for low speed and low pressure. For example, the main rotor of a hi h speed, high pressure device may have three to six threads and the gate rotor four to seven threads, .While for low pressure the main rotor may have two threads and the gate rotor three or four threads. Any of these combinations will operate satisfactorily and will have certain advantages, but it is believed that three threads on the main rotor and four threads on the gate rotor provide the best combination. This disclosure will therefore be directed to such a. combination but will not be limited thereto. Since the threads of these rotors are of fully generated form through most of their length, the rotors will drive each other like a set of gears. However, since in actual use the rotors usually operate without lubrication on the thread surfaces, timing gears are provided to hold the rotor threads in timed or spaced relation and there is usually no contact between the rotor threads when the device is in operation. Further, these rotors are of such shape that they provide accurate balance and extreme rigidity to eliminate contact with each other and with the housing during operation under heavy loads.

The principal object of this invention is to provide rotors for screw type compressors, blowers, pumps and similar devices having threads that form an unbroken seal throughout the compression area, form proper seals through the discharge area, and do not form closed pockets at the discharge end of the device.

Another important object is to provide rotors of the character described wherein the main rotor threads are generated by intersection protuberances lying slightly inside the perimetric tips of the gate rotor threads.

Another object is to provide helically threaded rotors of improved construction wherein the threads of the main rotor are not generated completely to the root of the threads.

Another object is to provide rotors for a screw type device with threads having a generated portion which extends from the suction end to the edge of the discharge port of the device and thereafter changes gradually to an arcuate thread at the extreme discharge end.

Another object is to provide an improved gate rotor having increased resistance to bending in the high pressure area.

Another object is to provide gate rotors of novel construction wherein the rotor threads are stronger and have greater resistance to deflection in the high pressure area.

Another object is to provide threaded rotors of improved design wherein the thread area exposed to high pressure air is reduced at the discharge end.

Another object is to provide rotors of the type described wherein there is a congruent surface seal of material width in the high pressure area when the main and gate rotor threads are in full mesh.

Another object is to provide for theoretically perfect sealing through the compression area of a screw type compressor or like device by the use of generated threads on the rotors, and to eliminate the seal pocket at the discharge end by gradually changing from generated threads to arcuate threads through the discharge area.

Another object is to eliminate the sealed pocket at the discharge end of such a device without the use of relief grooves, notches, ducts or by-passes.

Another object is to provide intermeshing threaded rotors that discharge all the air taken into the suction spaces thereof, there being no clearance spaces and/ or no re-expansion spaces.

Another object is to provide rotors of the above-dcscribed type wherein the extreme ends of the suction spaces do not become interposed between the discharge pocket and the discharge port.

Other objects and advantages of the invention will appear in the following description, reference being had to the several embodiments illustrated in the accompanying drawings in which:

FIG. 1 is a longitudinal sectional view of one form of screw type compressor embodying the present invention, the section being taken through the axes of the rotor members on the line A-A in FIG. 2.

FIG. 2 is a longitudinal sectional view taken through the axis of the main rotor on the line BB in FIG. 1 perpendicular to the plane of FIG. 1 and showing the suction and discharge ports of the compressor.

FIG. 3 is a perspective view of a pair of rotors per se embodying the invention and showing in particular the discharge ends of the rotors.

FIG. 4 is a fragmentary side view of a pair of generated rotors embodying the invention in mesh showing how they provide a seal at the intersection of the housing chambers.

FIG. 5 is a fragmentary perspective end view of a pair of conventional generated rotors in mesh showing the formation of a sealed pocket at the discharge end, the end wall which seals the end of the pocket not being shown.

FIG. 6 is a fragmentary side view of a pair of meshed rotors having arcuate threads throughout their length, showing openings or leakage paths at the intersection of the housing chambers.

FIG. 7 is a fragmentary perspective end view of a pair of rotors with arcuate threads, almost in full mesh, showing there are no sealed pockets at the discharge end. The normal end wall, not shown, would not seal these pockets.

FIGS. 8 to 15, inclusive, are transverse sectional outline views of meshed rotors illustrating the difference in action of generated threads and arcuate threads at the discharge ends of the rotors, FIGS. 8, 9, 10 and 11 showing a pair of generated rotors in various positions from full mesh to about 10 before full mesh, respectively, while FIGS. 12, 13, 14 and 15 show a pair of arcuate thread rotors in various positions from about 30 before full mesh to full mesh, respectively.

FIGS. 16 to 21, inclusive, are diagrams of rotor sections comprising what may be termed a nomenclature sheet, the preferred names, together with reference numbers of the various parts of the rotors being given as they are used throughout the specifications and claims. FIGS. 16, 18 and 20 are sectional views on the lines F-F and D--D in FIG. 22 and a discharge end view, respectively, of the gate rotor only, while FIGS. 17, 19 and 21 are corresponding sectional and discharge end views of the main rotor only.

FIG. 22 is a fragmentary longitudinal section through the rotors shown in FIG. 23, taken on line P-P in the latter figure, the rotors being shown untwisted for clarity.

FIG. 23 is an end view of the preferred form of rotors shown in FIG. 22, the dotted lines indicating the shapes of the rotors on line F-F in FIG. 22.

FIG. 24 is a fragmentary longitudinal section through a pair of rotors, in mesh, in which the transition from generated threads to arcuate threads is made in one step instead of gradually as in FIG. 22, the rotors being shown untwisted for clarity.

FIG. 25 is a fragmentary end view of a set of rotors of modified form. These rotors are similar to those of FIG. 23 except that the generating edges of the gate rotor threads lie slightly inwardly from the perimetric tips thereof and the main rotor is not generated completely to its root.

FIG. 26 is a fragmentary longitudinal section of the rotors shown in FIG. 25, taken on line RR in the latter figure, the rotors being shown untwisted for clarity. This view is the same as FIG. 22 except the main rotor hub is smaller and the outside diameter of the gate rotor is larger.

FIG. 27 is a fragmentary end view of a main rotor in which the arcuate surfaces forming the tips of the threads have their centers of curvature lying inside the pitch circle, the rotor being shown untwisted for clarity.

FIG. 28 is a fragmentary end view of a gate rotor which is complementary to the main rotor shown in FIG. 27.

FIG. 29 is a fragmentary end view of a main rotor in which the lands at the tips of the generated threads continue across the arcuate portions or discharge areas of the threads to the extreme discharge end of the rotor, the rotor being shown untwisted for clarity.

FIG. 30 is a fragmentary end view of a main rotor in which the arcuate or discharge sections are not tapered on their outside diameter. In such a modification the rotor 53 threads are thicker in the arcuate section. The rotor is shown untwisted for clarity.

FIG. 31 is a fragmentary end view of a gate rotor which is complementary to the main rotor shown in FIG. 30, the rotor being shown untwisted for clarity.

FIGS. 32 to 41, inclusive, are sectional outline views, fragmentary as respects the main rotor, of rotors of the preferred form in which the main rotor is generated to the root of its threads by the crest edges of the gate rotor and the gate rotor is complementary. FIGS. 32, 34, 36, 38 and 40 are a fragmentary discharge end View of the main rotor and fragmentary transverse sectional views thereof on lines CC, D-D, EE and FF in FIG. 22, respectively, while FIGS. 33, 35, 37, 39 and 41 are corresponding views of the complementary gate rotor.

FIGS. 42 to 51, inclusive, are views similar to FIGS. 32 to 41 of a modified form of rotors wherein the main rotor is generated almost to the root of its threads by the intersection protuberances on the gate rotor, there being small flat surfaces forming parts of the thread surfaces at the root of said main rotor threads and the gate rotor being complementary.

FIG. 52 is a sectional outline view of the modified rotors of FIG. 26, taken on line J-] in the latter figure, the gate rotor thread being in full mesh in the main rotor trough.

FIG. 53 is a View similar to that of FIG. 52, except in FIG. 53 the rotors are shown in a position wherein the main rotor thread is in mesh in the gate rotor trough.

FIG. 54 is another view similar to FIG. 52, except in FIG. 54 the rotors are shown in a position wherein the main rotor thread is just entering the gate rotor trough. A fragmentary showing of the housing at the intersection of the rotor chambers is included in this view.

FIG. 55 is a sectional outline view of the modified form of main rotor being generated by a tool simulating the intersection protuberances of the gate rotor. The tool is shown as having out about halfway down the side of one thread of the main rotor.

FIG. 56 is a fragmentary view similar to FIG. 55 except the tool is shown as just starting its out from the tip of the main rotor thread.

FIG. 57 is a fragmentary view similar to FIG. 55 except the entire side of the main rotor thread has been generated and the tool has just reached the small flat on the side of the thread at the root thereof and the generating cut is completed.

FIG. 58 is a fragmentary view similar to FIG. 55 except the generation of the side of the main rotor thread is completed and the tool is rolling across the land at the root of the main rotor with clearance for the chips as shown.

FIG. 59 is an enlarged fragmentary suction end view of the generated portion of the modified rotors of FIGS. 4-2 to 51, inclusive, showing the rotor threads in that position of rotation where they form a congruent seal zone between the small fiat surfaces.

FIG. 60 is a fragmentary discharge end View of the main rotor shown in FIG. 59, being shown untwisted for clarity.

FIGS. 61 and 62 are fragmentary side and top views, respectively, of the rotor thread shown in FIGS. 59 and 60, being shown untwisted for clarity.

It is important to note that the drawings are accurate scale representations of rotors embodying the invention, particularly as respects the sectional outline shapes of the rotor threads. Accordingly, in the interest of accuracy, shades lines have been omitted from many of the figures.

In the specifications and claims certain terms such as pockets, run-out, timing gears, timing, compression area and discharge area are used, and to render the meanings thereof clear the following definitions are set forth.

Pckets.The spaces or cavities formed by the coaction of the rotor threads in conjunction with the housing f5 chamber walls. These pockets are actually the spaces that are filled with the fluid being pumped. During operation of the device the pockets form continuously at the suction end of the rotors and vanish continuously at the discharge end thereof.

Rzm-out.This is the term used in connection with the pockets as they reach the discharge end of the rotors and decrease in size to zero, i.e., vanish, or run-out. At the suction end these pockets continue to fillwith the fluid being pumped until they reach maximum size. They are then disconnected from the suction port by the rotation of the rotors and begin to decrease in size and compress the fluid therein. Compression continues until the edge of the discharge port is reached when discharge of the fluid takes place. After passing the edge of the discharge port the pockets are no longer sealed because of the absence of the chamber walls but they continue to advance to the discharge end where they vanish or runout.

Timing gears.--Gears are used to synchronize the rotors and keep them in timed relation. The clearance between the rotor threads must be greater than the clearance between the gear teeth if contact between the rotor threads is to be avoided in operation. The clearance between the gear teeth may be .002" to .004" while the clearance between the rotor threads may be .020" to .040" depending upon the size of the device. Thus the rotor threads cannot contact each other as the threads are held in spaced relation by the timing gears.

T iming.-Timing is the act of setting the gears in relation to the rotor threads to eliminate contact between said threads. One of the timing gears is usually made separately from its hub and is adjustable with respect thereto to facilitate the timing operation when the device is assembled.

Compression area.This is the area of the rotors where compression takes place and is located between the lines K and L in FIGS. 2, 61 and 62. The compression area begins at K, or the suction end of the rotors, and extends to the edge of the discharge port at line L. After the tips of the rotor threads register with the edge of the discharge port internal compression no longer occurs, the fluid being free to enter the discharge. Since the rotors are of the full generated form through this area, the area could also be termed the generated area. For simplicity it is termed the compression area.

Discharge area.This the area of the rotors where discharge takes place and is located between the lines L and M in FIGS. 2, 61 and 62. Beginning at line L where the rotors are fully generated, the discharge area extends to the ends of the rotors at M where the rotors are fully arcuate on their tips. This transition from fully generated form to arcuate form occurs gradually from L to M, and in this area the flanks of the main rotor threads are generated and the tips are arcuate. Thus this discharge area cannot truly be called the arcuate area as the threads in this area are partially generated and partially arcuate.

Referring now to FIGS. 1 and 2, wherein the invention is shown, by way of example, as applied to screw type pump or compressor, the housing 10 of the device contains two parallel cylindrical chambers 12 and 14 disposed side by side in parallelism and merging into each other to form a common chamber, the cross section of which is somewhat in the form of a FIGURE 8. ()ne end of the housing is provided with an integral end wall 16 which forms one end wall of the chambers 12 and 14. The other end of the housing is formed by a removable end wall to enable insertion of a pair of mating helical screw thread rotor members 34 and 38 which are arranged to operated within rotor chambers 12 and 14, respectively. Rotor 34 is termed the main rotor, and has left-hand threads in the embodiment illustrated. Rotor 38 is termed the gate rotor and has threads which are complementary to those of the main rotor, i.e., right-hand.

The removable end wall of the housing is made in two parts in the form of re-entrant heads which are self centering. The re-entrant head 18 for the gate rotor chamber 14 is continuously circular on its outside diameter and fits the chamber without clearance. The re-entrant head 20 for the main rotor chamber 12 is also circular on its outside diameter except it has a concave niche formed in one side to allow it to be assembled into the housing beside the gate rotor re-entrant head. The reentrant heads 18 and 20 are held in proper relation to the housing by the'headplate 22. The housing end wall 16 is provided with two cylindrical bearing bores 24 and 26 which are concentric with the main rotor chamber 12 and the gate rotor chamber 14, respectively. Likewise, the re-entrant heads 18 and 20 are provided with cylindrical bearing bores 30 and 28, respectively, which are centrally located in their respective re-entrant heads.

Each of cylindrical bearing bores 24, 26, 28 and 30 is provided with a bearing bushing 32, which may be similar for all bearings. The main rotor 34 is fixedly attached to a shaft 36 and is centrally located in the main rotor chamber 12 by the bushing 32 in bearing bores 24 and 28. The gate rotor 38 is likewise fixedly attached to a shaft 40 and is centrally located in the gate rotor chamber 14 by the bushings 32 in bearing bores 26 and 30.

The main rotor shaft 36 has a timing gear 42 fixedly attached thereto while the gate rotor shaft 40 has a hub 44 fixedly attached thereto on which a gate rotor gear 46 is adjustably mounted. This provision for adjustment allows the rotor threads to be timed in spaced relationship.

There is a lateral discharge port 48 in the gear end of the housing and a lateral suction port 56, diagonally opposite, in the drive end of the housing. The exact shapes of these ports will be described later.

The rotor chambers 12 and 14 and the re-entrant heads 18 and 20 are slightly larger in diameter than the rotors 34 and 38 so that the rotors are centrally located in a positive manner and may operate with a minimum clearance. Common bearing bushings 32 are shown for reasons of simplicity but it will be understood that suitable bearings may be supplied to carry both the radial and the thrust loads which are developed in such a device.

The main rotor 34, as shown, has three circumferentially extending, evenly spaced helical threads 52 of identical contour, the exact shape of which is described hereinafter. The gate rotor 38, as shown, has four circumferentially extending, evenly spaced helical threads 54, the exact shape of which is also described later. The principal object of this invention being to provide theoretically perfeet sealing in the compression area K to L, and to eliminate sealed pockets at the discharge end of the rotors, that part of the invention, i.e., the rotors, will be described first with particular reference to FIGS. 4, 5, 6 and 7.

In the generated rotors of FIG. 4, the crest edges 56 of the gate rotor are shown as forming an unbroken seal from the root 68 of the thread of the main rotor 34 to its crest edge 58. Likewise the crest edges 58 of the main rotor form an unbroken seal across the trough 62 of the gate rotor. Thus there is no opening between the rotor threads at the point Where the crest edges 56 and 58 of the rotors meet to form the intersection '72 (FIGS. 1, 4 and 9). Together with the housing chambers intersection 74 (FIG. 9), the rotor threads and housing chambers form a theoretically perfect seal and the fluid being pumped is sealed against leakage between the forward high pressure pockets and the trailing low pressure pockets.

With the new rotor disclosed herein, the seal 72 at 74 (FIG. 9) exists throughout the compression area 61 (FIG. 2). This type of sealing is highly desirable in the compression area and its advantages form an important part of this invention. This seal forms at the suction end of the rotors and advances with the pockets to the discharge area 63 as the rotors revolve. Since there are no leakage openings between the forward high pressure pockets and the trailing low pressure pockets, true adiabatic compression is attained.

FIG. 6 shows rotors with arcuate threads throughout their length. Such rotors are disclosed by Nilsson in Patent No. 2,622,787. Suchj rotors have the disadvantage of creating a leakage opening at the point 76 (FIG. 6) where the rotor threads intersect. This type of scaling is highly undesirable in the compression area, and the present invention is intended to eliminate its disadvantages. Since the opening 80 (FIGS. 6 and 12) cannot be sealed by the intersection 74 of the housing chambers, there is thus created a leakage path from the high pressure end of the rotors to the suction end. This opening is fully described in Nilsson Patent No. 2,622,787, column 12. This type of device cannot produce fully adiabatic compression, and part of the power is lost through blowback and r e-compression.

FIG. 5 shows a pair of fully generated rotors wherein the generated form is continued through the discharge area to the extreme discharge end. With the necessary end wall (not shown), a closed pocket 78 is formed as the rotors revolve, which pocket is a disadvantage as it creates excessive pressure, temperature, noise and bearing loads and reduces the capacity and speed of operation. Many attempts have been made to vent this pocket by various grooves in the rotor, or end Wall, but these vents usually do not truly serve the purpose because of their limited capacity; furthermore, they usually create a new leakage path or carry high pressure fluid to the suction side.

FIG. 7 shows the extreme end of arcuate rotors as shown in FIG. 6, the necessary end wall not being shown. Through the discharge area only, the opening 80 is a major advantage as it eliminates the formation of a sealed pocket. Thus, in this invention, the generated rotor form is used in the compression area where perfect scaling is an advantage, while through the discharge area the generated form gradually changes to the arcuate form to eliminate the sealed pocket at the discharge end. Since the work required of the rotors is different at the suction and discharge ends, to select different rotor forms for the suction and discharge ends and to blend these two forms in such a manner that no advantages are lost at either end, and, also, that no disadvantages are retained, is a substantial improvement. This transition from the generated form to the arcuate form should occur completely within the discharge port area to prevent possible back flow to a trailing pocket as before described.

FIGS. 8 to 11, inclusive, show the preferred form of generated rotor threads in the compression area 61 between K and L in FIG. 2, and FIGS. 12 to 15, inclusive, show the preferred arcuate rotor form at the end of the discharge area 63.

FIG. 8 shows a main rotor thread in full mesh with a gate rotor trough. It will be noticed that the surface of the main rotor thread it is not congruent with the gate rotor trough because of the generated form. The pocket has almost run out but is still closed.

FIG. 9 shows the main rotor thread just entering the gate rotor trough the motors being about 30 before full mesh position. The pocket has just closed, and any fluid trapped therein can only be discharged through the end of the pocket which is usually enclosed by an end wall.

In FIG. 10 the rotor threads are further in mesh, about 20 before full mesh position, and the pocket is disappearing but is still sealed by the threads and end wall.

In FIG. 11 the threads are almost in full mesh but the pocket is still sealed.

FIG. 12 shows the discharge end of the rotors, and also shows the intersection of the housing chambers to clarify the opening of the rotor threads. In this FIGURE the rotor threads are entering into mesh, with the rotors about 30 before full mesh position as in FIG. 9, but there is no closed pocket when the necessary end wall is added.

In FIG. 13 the rotor threads are further in mesh, as in FIG. 10, but there is still no closed pocket, the opening being on the side of the threads.

In FIG. 14 the rotors are almost in full mesh, as in FIG. 11, but there is still no sealed pocket, there still being an opening on the side of the threads.

In FIG. 15 the rotor threads are in full mesh and the pocket has completely disappeared. The main rotor thread is congruent with the gate rotor trough. A comparison of FIG. 15 with FIG. 8 shows the difference between generated threads and arcuate threads. Further rotation of the rotors in FIG. 15 will transfer the seal to the left side of the main rotor thread, or the reverse of FIGS. 14, 13 and 12.

In summary, the rotors may be described as being generated through the compression area 61 (K to L, FIG. 2), where they are similar in cross section to the rotors of Whitfield Patent No. 2,287,716, while through the discharge area 63 (L to M, FIG. 2) a transition occurs wherein the rotors change gradually from a generated form to an arcuate form at the extreme end. The transition portions or discharge areas of the preferred rotors are illustrated in FIGS. 22, 23 and 32 to 41, inclusive.

As shown in FIG. 32, the tip 51 of the main rotor thread may be truly arcuate, although slight deviations from the true are will operate successfully. To simplify this disclosure, the tips of the threads are termed arcuate and the complementary surfaces of the troughs in the gate rotor are also termed arcuate. In FIG. 32, the arcuate tip 51 has its center of curvature substantially on the pitch circle 82 while the flanks 59 are generated by the crest edges 56 of the gate rotor threads (FIG. 33).

In FIGS. 34, 36 and 38, the arcuate tip is still designated 51 and its center of curvature still lies substantially on the pitch circle. However, the'length of the radius forming the tip 51 changes in length between the discharge end of the rotor and the compression area, being shortest at the extreme end of the rotor, thereby producing a tapering or decrease in height of the thread through the discharge area. Likewise, the width of the arcuate tip 51 changes in width between the discharge end of the rotor and its intersection with the tip 53 in the compression area, being widest at the extreme end of the rotor. This is more clearly shown in FIGS. 61 and 62,

from which it is also evident that the decrease in height of the thread is less than half the height of the thread in the compression area.

In FIGS. 33, 35, 37 and 39, the root 49 of the gate rotor trough is also arcuate and is complementary to the arcuate tip portion 51 of the main rotor, the depth of the trough tapering or decreasing through the discharge area just as the height of the main rotor thread decreases. The generated flanks '57 of the gate rotor threads shown in FIGS. 35, 37 and 39 are generated by the generating edges 70 of the main rotor threads shown in FIGS. 24, 36 and 38.

FIG. 24 illustrates a modification of the preferred forms of rotors wherein the change from a fully generated section to an arcuate section occurs as a sharp step rather than gradually. The rotor threads would thus have shapes similar to FIGS. 32 and 33 throughout the discharge area 63", and would have shapes as in FIGS. 40 and 41 throughout the compression area 61". The modification shown in FIG. 24 is not preferred and its use depends upon the facilities for manufacturing.

FIG. 27 shows the arcuate end of a main rotor thread where the center of curvature of the arc is inside the pitch circle 82. Such. an arc cannot be congruent with the gate rotor trough as the generating corners 70 will not roll out of the gate rotor trough if the latter is made as shown in FIG. 28. Likewise, the center of curvature cannot lie substantially outside the pitch circle or the device will likewise become inoperative.

In FIG. 29 the land 64 at the tip of the compression area of the main rotor thread is carried on through the discharge are. In the discharge area the land 64 could be wider or narrower than the land in the compression area. In any event, such a continuous land has an advantage as it provides a seal of material Width with the housing, and also is easier to hold to exact size.

FIG. 30 shows a rotor thread where the discharge area is not tapered on the outside diameter. The arcuate end is increased in height to the height of the compression area, and is also increased in thickness greater than that of the generated portion of the thread. A gate rotor thread complementary to the main rotor shown in FIG. 30 is shown in FIG. 31. The threads of FIGS. 30 and 31 would be difiicult to machine, and probably would not be advantageous unless a straight bore in the main rotor chamber would be desirable.

FIGS. 25, 26, 52, 53, 54, 42 to 51, inclusive, and 59 to 62, inclusive, show a pair of generated rotors of moditied form wherein parts corresponding to those of the preferred form are designated by the same numerals but with prime markings. with or without the arcuate thread tips in the discharge area end section, but if used without the arcuate end section they will produce a closed pocket. As shown in FIG. 52, the trough 62' of the gate rotor 38' is similar in sectional outline to the trough 62 of FIGS. 16 and 41, and is generated by the crest edges 58' of the main rotor 34. Outside the trough area of the gate rotor the crest edges are broken to form flats S6 which may lie partially or wholly outside the pitch circle. The flats form new generating'edges or intersection protuberances 84 which become the new sealing edges instead of the crest edges 56 as used in the preferred form. There are also flats 88 at the roots of the main rotor threads which become congruent with the flats 86 on the gate rotor, as shown in FIG. 59, as the threads roll into mesh.

While the modified form of rotors has a slightly greater capacity than the preferred form, the principal advantage lies in its ease of machining. This is shown in FIGS. to 58, inclusive. The root portion 68 and the flats 88 of the main rotor are finished first in any suitable manner before the start of the generating operation. A generating tool 92 is then provided as shown in FIGS. 55 to 58, inclusive, and is rotated in timed relation with the rotor. The cut occurs from the tip of the thread to its root as shown by the arrows. Suitable gears properly control the rotation of the tool and rotor. The tool bit 94 cuts out at the fiat SS and rolls across the root 623' of the trough there being sufficient clearance between the bit 94 and rotor (FIG. 58) to provide for chip clearance. This chip clearance is quite important as the bit 94 would be broken if it rolled on the root of I the main rotor and chips lodged therebetween.

FIGS. 42 to 51 are similar to FIGS. 32 to 41 except that the modified rotors are shown. In these modified rotor sections, the discharge area and the compression area are substantially the same as in the preferred sections. However, in the modified form the gate rotor is larger than its pitch circle and there is a small flat surface 86 between the generating edge 84 and the outside diameter. On the main rotor the hub diameter is smaller than its pitch circle, the sides of the threads are generated substantially to the pitch circle, and there is a small flat 88 between each generated surface and the root surface. These flat surfaces 86 and 38 should not be confused with other rotors wherein the crest edges of the gate rotor threads are changed from sharp edges. For example, in Montelius Patents Nos. 1,821,523 and 2,198,786 there is shown a gate rotor with the crest edges broken. However, among other descriptions these are described as helical gear surfaces, the surfaces rolling on one another in the manner of intermeshing helical gears. Since these Montelius patents include no timing gears, it is intended that the helical gear surfaces serve the purpose of timing gears so that their shape must be similar to gear teeth.

Such rotors may be used In Lysholm Patent No. 2,174,522 the crest edges of the gate rotor are rounded off to eliminate undesirable sharp edges. In Whitfield Patent No. 2,486,770 the crest edges of both rotors are rounded to produce arc generation. Helical screw devices similar to those of the Montelius Patents Nos. 1,821,523 and 2,198,736 and Lysholm Patent No. 2,174,522 and others having gate rotors with rounded crest edges on the gate rotor and no timing gears are used only as liquid pumps since devices of this type cannot be operated at high speed without lubrication on the rotor surfaces.

The device of the present invention is intended primarily as a compressor and the rotors usually operate at high speed without lubrication, therefore, timing gears are necessary and the primary object in breaking the gate rotor crest edges is to provide rotors that are easier to machine accurately while maintaining unbroken seal lines.

In the modified rotor form, shown enlarged in FIG. 59, the surfaces 86 and 38 are flats and are located at such angles that they will become congruent during certain periods of rotation and form an eflicient seal in this critical area. This is a very important part of this invention.

Any type of rounded corners or gear teeth form will produce a sliding line seal instead of a surface seal, as here proposed. 01" course, the flat surfaces 86 and 88 would not be suitable for driving the rotors, and it is not intended that they make contact or be used to serve the purpose of gears. This modification eliminates the necessity of generating completely to the root of the main rotor and provides chip clearance for the cutter as shown at Qt) in FIG. 58. The flats 88 and the root 68' are usually cut before the generating operation is started. In this manner the bit 94 has a place to run out and the chip is cut entirely free. If the bit 90 were to cut into a fillet as in the Montelius, Lysholm and Whitfield patents above mentioned, the chip would not be cut free and breakage of the bit could occur. Also, by providing the flats 88 and positioning them at the most advantageous angle to the rotor thread, it is easier to properly match the generated sides of the thread with the flats 38. This is very important as it is necessary to form an accurate intersection without breaking the bit 94.

A machine capable of generating both rotors is shown in Whitfield Patent No. 2,792,763.

The tool herein proposed for cutting the main rotor is shown at 92 in FIG. 55. As previously proposed in the above mentioned generating machine, Patent No. 2,792,763, both sides of all the threads on a main rotor were generated at one pass. In this instance the tool 92 generates only one side of all the threads at one pass. The rotor is then turned end for end and the other side of all the threads are generated. In cutting both sides of each thread at one pass, it is necessary to cut from the tip of the thread to the root on one side and to cut from the root to the tip on the other side of each thread. It is believed to be more practical to cut the sides of the threads by starting each cut from the tip as it is easier to get both sides exactly alike and the thicknes of the threads is more easily controlled. The lands 68 at the root of the main rotor threads 52' (FIG. 59) are helical cylindrical surfaces and are uniform in width throughout the length of the rotor. Likewise, the lands 66' on the tips of the gate rotor threads 54' are also helical cylindrical surfaces of uniform width throughout the length of the rotor, and these lands 66' form a rolling seal with lands 68' on the main rotor. To produce the main rotor, it may be generated throughout its length as in FIG. 8 and, after being generated, the tip of each thread in the discharge area could be altered as shown generally in FIGS. 32, 34, 36 and 38. The gate rotor could be generated as shown in FIG. 8 through the compression area only. The remainder of the rotor, or the discharge area, could be machined by duplication using a master template, or generated with a proper cutter having a compound movement.

Housings for devices of this general nature are well known and need not be described in detail. The discharge port 48 (FIG. 2) is located at the tapered end of the rotors and is generally triangular in shape, one of the sides being formed by the end wall 16 while the other two sides follow the tips of the threads on the main and gate rotors when they are so located that the compression in the advancing pockets has raised the pressure to the desired discharge pressure. Further rotation of the rotors opens the pocket to the discharge port and the volume of the pocket is discharged. The widest portion of the discharge port would be at line L in FIG. 2.

The defining edges of the suction port are also triangular, one side being formed by the re-entrant heads 18 and 20 while the other two sides follow the tips of the main and gate rotor threads when said threads are advanced to the position Where they form the maximum sized pocket. In FIG. 1, wherein the direction of rotation is indicated by arrows, the suction port would be on the front or upper side at the left end and the discharge port, being diagonally opposite, would be on the back or under side at the right-hand end.

What is claimed is:

1. In a compressor or similar device of the type having (a) a housing with intersecting cylindrical rotor chambers and suction and discharge ports arranged diagonally opposite each other near the ends of said hous ing, and

(12) a pair of complementary helically threaded rotors consisting of a main rotor and a gate rotor each having a plurality of threads with crest edges and troughs,

(c) said rotors being rotatably supported within the chambers of said housing and cooperating with each other and the housing to form pockets as the suction end of the rotors for receiving fluid through said suction port, to advance said pockets and the fluid therein axially along the rotors and to exhaust the fluid at the discharge end of the rotors through the the discharge port as the rotors revolve about the axes thereof,

(d) the threads of each rotor having sealing engagement with the troughs of the mating rotor throughout the lengths of the rotors, and also having sealing engagement with the housing throughout at least those portions of the lengths of the threads which extend between the suction port and the discharge port, and

(e) the threads of the main rotor lying substantially outside the pitch circle thereof and the threads of the gate rotor lying substantially inside the pitch circle thereof;

the improvement which comprises:

(1) each of said rotors having axially extending compression and discharge areas wherein the rotor threads are of different shapes, the compression areas extending from the suction ends of the rotors to the leading edge of the discharge port and the discharge areas extending from said edge to the discharge ends of the rotors,

(2) the threads of the main rotor having lands at the tips thereof of substantially uniform width and being of generated form substantially from tip to root thereof throughout the axial length of the compression area and having arcuate tips in the discharge area which gradually increase in arcuate Width toward the discharge end of the rotor, the flanks of the threads in the discharge area between the arcuate tips and the roots thereof being of generated form, the generated portions of the main rotor threads being generated by the crest edges of the gate rotor threads and the arcuate tips of the main rotor threads having their centers of curvature substantially on the pitch circle of said threads midway between the sides of the threads, and

(3) the threads of the gate rotor being complementary to those of the main rotor,

(4) whereby the threads of the main and gate rotors cooperate to form an unbroken seal throughout the compression areas, form proper seals through the discharge area, and do not form closed pockets at the discharge ends of the rotors.

2. In a compressor or similar device of the type having (a) a housing with intersecting cylindrical rotor chambers and suction and discharge ports arranged diagonally opposite each other near the ends of said housing, and

(b) a pair of complementary helically threaded rotors consisting of a main rotor and a gate rotor each having a plurality of threads with crest edges and troughs, I

(c) said rotors being rotatably supported within th chamber of said housing and cooperating with each other and the housing to form pockets at the suction end of the rotors for receiving fluid through said suction port, to advance said pockets and the fluid therein axially along the rotors and to exhaust the fluid at the discharge end of the rotors through the discharge port as the rotors revolve about the axes thereof,

(d) the threads of each rotor having sealing engagement with the troughs of the mating rotor throughout the lengths of the rotors, and also having sealing engagement with the housing throughout at least those portions of the lengths of the threads which extend between the suction port and the discharge port, and

(e) the threads of the main rotor lying substantially outside the pitch circle thereof and the threads of the gate rotor lying substantially inside the pitch circle thereof;

the improvement which comprises:

(1) each of said rotors having axially extending compression and discharge areas wherein the rotor threads are of diiferent shapes, the compression areas extending from the suction ends of the rotors to the leading edge of the discharge port and the discharge areas extending from said edge to the discharge ends of the rotors,

(2) the threads of the main rotor having lands at the tips thereof of substantially uniform width and being of generated form substantially from tip to root thereof and of uniform height throughout the axial length of the compression area and having arcuate tips throughout the axial length of the discharge area, the flanks of said threads in the discharge area between the arcuate tips and the roots thereof being of generated form, the generated portions of said threads being generated by the crest edges of the gate rotor threads,

(3) the outside diameter of said arcuate tips tapering uniformly toward the discharge end of the main rotor, t

(4) the centers of curvature of the arcs of said arcuate tips lying substantially on the pitch circle of said main rotor midway between the sides of the threads, and

(5 the threads of the gate rotor being complementary to those of the main rotor,

(6) whereby the threads of the main and gate rotors cooperate to form an unbroken seal throughout the compression areas, form proper seals through the discharge area, and do not form closed pockets at the discharge ends of the rotors.

3. In a compressor or similar device of the type having (a) a housing with intersecting cylindrical rotor chambers and suction and discharge ports arranged diago id nally opposite each other near the ends of said housing, and

(b) a pair of complementary helically threaded rotors consisting of a main rotor and agate rotor each having a plurality of threads with crest edges and troughs,

(c) said rotors being rotatably supported within the chambers of said housing and cooperating with each other and the housing to form pockets at the suction end of the rotors for receiving fluid through said suction port, to advance said pockets and the fluid therein axially along the rotors and to exhaust the fluid at the discharge end of the rotors through the discharge port as the rotors revolve about the axes thereof,

(d) the threads of each rotor having sealing engagement with the troughs of the mating rotor throughout the lengths of the rotors, and also having sealing engagement with the housing throughout at least those portions of the lengths of the threads which extend between the suction port and the discharge port, and

(e) the threads of the main rotor lying substantially outside the pitch circle thereof and the threads of the gate rotor lying substantially inside the pitch circle thereof;

the improvement which comprises:

(1) each of said rotors having axially extending compression and discharge areas wherein the rotor threads are of different shapes, the compression areas extending from the suction ends of the rotors to the leading edge of the discharge port and the discharge areas extending from said edge to the discharge ends of the rotors,

(2) the threads of the main rotor having lands at the tips thereof of substantially uniform width and being of generated form substantially from tip to root thereof and of uniform height throughout the axial length of the compression area and having arcuate tips throughout the axial length of the discharge area, the flanks of said threads in the discharge area between the arcuatetips and the roots thereof being of generated form, the generated portions of said threads being generated by the crest edges of the gate rotor threads,

(3) the outside diameter of said arcuate tips tapering uniformly toward the discharge end of the main rotor,

(4) the intersections between said arcuate tips and the flanks of the main 'rotor threads forming generating edges,

(5) the troughs of the gate rotor being generated by the crest edges of the main rotor threads throughout the axial length of the compression area of the gate rotor and changing gradually throughout the axial length of the discharge area of said rotor from generated shape to a fully arcuate shape, the generated portion of said troughs in the discharge area of said rotor being generated by the generating edges of the main rotor threads,

(6) the troughs of the gate rotor in the discharge area having arcuate hoot portions the radii of which decrease uniformly toward the discharge end of said gate rotor,

(7) the centers of curvature of the arcs of said arcuate tips of the main rotor threads and said arcuate root portions of the gate rotor troughs lying substantially on the pitch circles of said rotors midway between the sides of said threads and troughs,

(8) whereby the threads of the main and gate rotors cooperate to form an unbroken seal throughout the compression areas, form proper seals through the discharge area, and do not form closed pockets at the discharge ends of the rotors,

4. In a compressor or similar device of the type having (a) a housing with intersecting cylindrical rotor chambers and suction and discharge ports arranged diagonally opposite each other near the ends of said housing, and

(b) a pair of complementary helically threaded rotors consisting of a main rotor and a gate rotor each having a plurality of threads and troughs,

(c) said rotors being rotatably supported within the chambers of said housing and cooperating with each other and the housing to form pockets at the suction end of the rotors for receiving fluid through said suction port, to advance said pockets and the fluid therein axially along the rotors and to exhaust the fluid at the discharge end of the rotors through the discharge port as the rotors revolve about the axes thereof,

(d) the threads of each rotor having sealing engagement with the troughs of the mating rotor throughout the lengths of the rotors, and also having sealing engagement with the housing throughout at least those portions of the lengths of the threads which extend between the suction port and the discharge port,

(2) the threads of the main rotor lying substantially outside the pitch circle thereof and haivng perimetric tips with crest edges, and

(f) the threads of the gate rotor lying substantially inside the pitch circle thereof;

the improvement which comprises:

(1) each of said rotors having axially extending compression and discharge areas wherein the rotor threads are of different shapes, the compression areas extending from the suction ends of the rotors to the leading edge of the discharge port and the discharge areas extending from said edge to the discharge ends of the rotors,

(2) the threads of the gate rotor having cut-away crest edges forming relatively narrow flat surfaces, the intersections between said flat surfaces and the sides of the gate rotor threads forming intersection protuberances,

(3) the threads of the main rotor having lands at the tips thereof of substantially uniform width and being of generated form substantially from tip to root thereof and of uniform height throughout the axial length of the compression area and having arcuate tips throughout the axial length of the discharge area, the flanks of said threads in the discharge area between the arcuate tips and the roots thereof being of generated form, the generated portions of said threads being generated by the intersection protuberances of the gate rotor threads,

(4) the outside diameter of said arcuate tips tapering uniformly toward the discharge end of the main rotor,

(5) the centers of curvature of the arcs of said arcuate tips lying substatntially on the pitch circle of said main rotor midway between the sides of the threads,

(6) the sides and flanks of the main rotor threads also having relatively narrow flat surfaces adjacent the roots of said threads which operate congruently with the flat surfaces formed by the cut-away crest edges of the gate rotor threads, and

(7) the threads of the gate rotor being complementary to those of the main rotor,

(8) whereby the threads of the main and gate rotors cooperate to form an unbroken seal throughout the compression areas, form proper seals through the discharge area, and do not form closed pockets at the discharge ends of the rotors, and the relatively narrow fiat surfaces adjacent the roots of the main rotor threads provide run-out clearance for a generating tool.

5. The improvement defined in claim 4 which is further characterized by (l) the troughs of the gate rotor being generated by the crest edges of the main rotor threads throughout the axial length of the compression area of the gate rotor and changing gradually throughout the axial length of the discharge area of said rotor from generated shape to a fully arcuate shape, the generated portion of said troughs in the discharge area being generated by the edges formed by the intersections between the arcuate tips and the flanks of the main rotor threads,

(2) the troughs between the gate rotor threads in the discharge area have arcuate root portions the radii of which decrease uniformly toward the discharge end of said gate rotor, and

(3) the centers of curvature of the arcs of said arcuate root portions of the gate rotor troughs lying substantially on the pitch circle of said gate rotor midway between the sides of the troughs.

6. The improvement defined in claim 4 which is further characterized by (1) the flat surfaces at the cut-away crest edges of the gate rotor threads lying at least partially outside the pitch circle of said gate rotor, and

(2) the flat surfaces adjacent the roots of the main rotor threads lying at least partially inside the pitch circle of said main rotor.

7. In a pump having a housing provided with intersecting cylindrical rotor chambers and suction and discharge ports arranged diagonally opposite each other adjacent the ends of the housing, and a pair of mating helically threaded rotors consisting of a main rotor and a gate rotor, each rotor having a plurality of threads with crest edges and troughs, said rotors being rotatably supported within the chambers of said housing and cooperating with each other and said housing to form pockets at the suction end of the rotors for receiving fluid through said suction port, to advance said pockets and the fluid therein axially along the rotors and to exhaust the fluid at the discharge end of the rotors through the discharge port as the rotors revolve in opposite directions about the axes thereof, the threads of each of said rotors having sealing engagement with the troughs of the mating rotor within which troughs said threads are received as the rotors are rotated to advance the pockets therealong;

each of said rotors haivng axially extending compression and discharge areas wherein the rotor threads are of different shapes, the discharge area being at the discharge end of the housing and having a length substantially equal to the axial dimension of the discharge port;

the main rotor being characterized by having throughout its length lands of substantially uniform width at the roots of the threads thereof, and relatively small flats connecting said lands with the sides of said threads, said flats providing run-out clearance for a generating tool, the sides of said threads from the crest edges and generating edges to the flats being of generated form;

the main rotor threads also having lands at the tips thereof of substantially uniform width throughout the compression area and non-uniform Width arcuate tips throughout the discharge area, the centers of curvature of the arcuate tips lying substantially on the pitch circle of the main rotor midway between the sides of the threads and the outside diameter of said arcuate tips decreasing toward the discharge end of the rotor; and

the gate rotor being characterized by having substantially uniform lands at the tips of the threads thereof, the crest edges of said threads being cut away in a substantially angular manner to form relatively small flats and to produce generating edges at the intersections between said flats and the sides of the troughs for generating the sides of the main rotor threads, said flats being of substantially the same size as the flats at the roots of the main rotor threads and formed to operate congruently therewith during rotation of the rotors, and the troughs of the gate rotor between said flats being generated by the crest edges of the main rotor threads throughout the compression area and by the generating edges of said threads throughout the discharge area to form an unbroken seal line between the rotors.

8. In a pump having a housing provided with intersecting cylindrical rotor chambers and suction and discharge ports arranged diagonally opposite each other adjacent the ends of the housing, and a pair of mating helically threaded rotors consisting of a main rotor and a gate rotor, each rotor having a plurality of threads with crest edges and troughs, said rotors being rotatably supported within the chambers of said housing and cooperating with each other and said housing to form pockets at the suction end of the rotors for receiving fluid through said suction port, to advance said pockets and the fluid therein axially along the rotors and to exhaust the fluid at the discharge end of the rotors through the discharge port as the rotors revolve in opposite directions about the axes thereof, the threads of each of said rotors having sealing engagement with the troughs of the mating rotor within which troughs said threads are received as the rotors are rotated to advance the pockets therealong;

each of said rotors having axially extending compression and discharge areas wherein the rotor threads are of different shapes, the compression and discharge areas extending toward one another from the suction and discharge ends, respectively, of the pump housing, the intersection between the compression areas and the discharge areas being substantially coplanar with the leading edge of the discharge port intermediate the ends of the rotors;

the main rotor being characterized by a gradual change in shape of the threads thereof in the discharge area, said threads changing from a generated form at the intersection between the compression and discharge areas to a substantially arcuate form at the discharge end of the rotor so as to provide said threads with arcuate tips throughout the discharge area, the centers of curvature of said arcuate tips lying substantially on the pitch circle of said rotor midway between the sides of the threads and the length of the radii forming said arcuate tips increasing in length from the discharge end of the rotor to the intersection between the compression and discharge areas; H the troughs at the roots of the main rotor threads being substantially uniform throughout the axial length of the rotor, and each of the main rotor threads having a land of uniform width at the tip thereof throughout the compression area; the width and height ofthe arcuate tips of the main rotor threads changing continuously through the discharge area, being Widest and lowest at the discharge end of the rotor, said arcuate tips blending with the lands at the tips of the threads at the intersection between the compression and discharge areas; the sides of the main rotor threads in the compression area and the flanks of said threads in the discharge area being generated by the crest edges of the gate rotor, the intersections between the arcuate tips and the generated flanks of said threads in the discharge area forming generating edges for generating the sides of the troughs of the gate rotor in the discharge area of said gate rotor; and the gate rotor being complementary to the main rotor. 9. The pump defined in claim 8 which is further characterized by the crest edges on the main rotor threads which are in sealing engagement with the troughs of the gate rotor through the compression area being spaced uniformly throughout said area, and the generating edges of the main rotor threads which have sealing engagement with the troughs of the gate rotor in the discharge area being spaced progressively further apart from the inter! section between the compression and discharge areas to the discharge end of the main rotor.

10. In a pump having a housing provided with intersecting cylindrical rotor chambers and suction and discharge ports arranged diagonally opposite each other adjacent the ends of the housing, and a pair of mating helically threaded rotors consisting of amain rotor and a gate rotor, each rotor having a plurality of threads with crest edges and troughs, said rotors being rotatably supported within the chambers of said housing and cooperating with each other and said housing to form pockets at the suction end of the rotors for receiving fluid through said suction port, to advance said pockets and the fluid therein axially along the rotors and to exhaust the fluid at the discharge end of the rotors through the discharge port as the rotors revolve in opposite directions about the axes thereof, the threads of each of said rotors having sealing engagement with the troughs of the mating rotor within which troughs said threads are received as the rotors are rotated to advance the pockets therealong;

each of said rotors having axially extending compression and discharge areas wherein the rotor threads are of different shapes, the discharge areas of said rotors being adjacent the discharge end of the housing and having lengths substantially equal to the axial dimension of the discharge port;

the main rotor being characterized by having cylin-.

drical lands of substantially uniform width at the roots of the threads thereof throughout the length of said rotor and relatively small flats connecting said lands with the sides of said threads, said flats providing run-out clearance for a generating tool, the main rotor threads also having lands at the tips thereof of substantially uniform width throughout the compression area and non-uniform width arcuate tips throughout the discharge area, the centers of curvature of the arcuate tips lying'substantially on the pitch circle of the main rotor midway between the sides of the threads and the length of the radii forming said arcuate tips decreasing toward the discharge end of the rotor; the sides of the main rotor threads in the compression area and the flanks of said threads between the arcuate tips and the flats in the discharge area being generated by generating edges of the gate rotor; and the gate rotor being complementary to the main rotor. 11. In a pump having a housing provided with intersecting cylindrical rotor chambers and suction and discharge ports arranged diagonally opposite each other adjacent the ends of the housing, and a pair of mating helically threaded rotors consisting of a main rotor and a gate rotor, each rotor having a plurality of threads with crest edges and troughs, said rotors being rotatably supported within the chambers of said housing and cooperating with each other and said housing to form pockets at the suction end of the rotors for receiving fluid through said suction port, to advance said pockets and the fluid therein axially along the rotors and to exhaust the fluid at the discharge end of the rotors through the discharge port as the rotors revolve in opposite directions about the axes thereof, the threads of each of said rotors having sealing engagement with the troughs of the mating rotor within which troughs said threads are received as the rotors are rotated to advance the pockets therealong;

each of said rotors having axially extending compression and discharge areas wherein the rotor threads are of different shapes, the discharge areas of said rotors being adjacent the discharge end of the housing and having lengths substantially equalto the axial dimension of the discharge port;

the gate rotor being characterized by having uniform lands at the tips of the threads thereof throughout the length of said rotor and by having the crest edges of said threads cut away in a generally angular manner to form relatively small flats, the intersections between said flats and the concave surfaces of the troughs of said rotor forming generating edges; the troughs of the gate rotor through the compression area being uniform and generated by the crest edges of the main rotor and the troughs through the discharge area being non-uniform and having arcuate surface portions in the centers of said troughs which blend axially into the generated troughs of the compression area, the centers of curvature of the arcuate portions of said troughs lying substantially on the pitch circle of the gate rotor midway between the sides of the troughs and the length of the radii forming said arcuate portions decreasing through the discharge area toward the discharge end of the rotor; the flanks of the gate rotor threads between the flats and the arcuate portions of the troughs in the discharge area being generated by the generating edges of the main rotor threads; and the main rotor being complementary to the gate rotor. 12. In a pump having a housing provided with intersecting cylindrical rotor chambers and suction and discharge ports arranged diagonally opposite each other adjacent the ends of the housing, and a pair of mating helically threaded rotors consisting of a main rotor and a gate rotor, each rotor having a plurality of threads with crest edges and troughs, said rotors being rotatably supported within the chambers of said housing and cooperating with each other and said housing to form pockets at the suction end of the rotors for receiving fluid through said suction port, to advance said pockets and the fluid therein axially along the rotors and to exhaust the fluid at the discharge end of the rotors through the discharge port as the rotors revolve in opposite directions about the axes thereof, the threads of each of said rotors having sealing engagement with the troughs of the mating rotor within which troughs said threads are received as the rotors are rotated to advance the pockets therealong;

each of said rotors having axially extending compression and discharge areas wherein the rotor threads are of different shapes, the junction between the compression and discharge areas of said rotors being substantially coplanar with the leading edge of the discharge port, and there being an abrupt change in shape of the rotor threads at said junction;

the main rotor being characterized by threads having tips of uniform and substantially arcuate shape throughout the discharge area, the centers of curvature of said arcuate tips lying substantially on the pitch circle of said rotor midway between the sides of the threads, said threads also having substantially arcuate tips throughout the compression area with the centers of curvature of said tips lying on the axis of the rotor;

the sides of the main rotor threads in the compression area and the flanks of said threads between the arcuate tips and the roots in the discharge area being generated by the crest edges of the gate rotor; said main rotor threads being of substantially uniform thickness at the pitch circle throughout the length 29 of the main rotor but of greater height through the compression area than through the discharge area of said rotor; and the gate rotor being complementary to the main rotor. 13. In a pump having a housing provided with intersecting cylindrical rotor chambers and suction and discharge ports arranged diagonally opposite each other adjacent the ends of the housing, and a pair of mating helically threaded rotors consisting of a main rotor and a gate rotor, each rotor having a plurality of threads with crest edges and troughs, said rotors being rotatably supported within the chambers of said housing and cooperating with each other and said housing to form pockets at the suction end of the rotors for receiving fluid through said suction port, to advance said pockets and the fluid therein axially along the rotors and to exhaust the fluid at the discharge end of the rotors through the discharge port as the rotors revolve in opposite directions about the axes thereof, the threads of each of said rotors having sealing engagement with the troughs of the mating rotor within which troughs said threads are received as the rotors are rotated to advance the pockets therealong;

each of said rotors having axially extending compression and discharge areas wherein the rotor threads are diiferent shapes, the discharge areas of said rotors being adjacent the discharge end of the housing and having lengths substantially equal to the axial dimension of the discharge port; tl e main rotor being characterized by having uniform lands at the roots of the threads thereof throughout the length of said rotor while the outside diameter of the tips of said threads tapers through the discharge area toward the discharge end of the rotor, the tapered portions of the threads having arcuate tips the centers of curvature of which lie substantially on the pitch circle of said rotor midway between the sides of the threads, the length of the radii forming said arcuate tips decreasing through the discharge area toward the discharge end of the rotor; the sides of the main rotor threads in the compression area and the flanks of said threads between the arcuate tips and the lands in the discharge area being generally convex; and the gate rotor being complementary to the main rotor to form substantially unbroken seal lines and run the pockets out to zero.

References Cited in the file of this patent UNITED STATES PATENTS 2,174,522 Lysholm Oct. 3, 1939 2,198,786 Montelius Apr. 30, 1940 2,287,716 Whitfield June 23, 1942 2,369,539 Delamere Feb. 13, 1945 2,410,341 Delamere Oct. 29, 1946 2,473,234 Whitfield June 14, 1949 2,486,770 Whitfield Nov. 1, 1949 2,622,787 Nilsson Dec. 23, 1952 2,652,192 Chilton Sept. 15, 1953 2,922,377 Whitfield Jan. 26, 1960 FOREIGN PATENTS 464,475 Great'Britain Apr. 16, 1937 588,287 Great Britain May 19, 1947 716,910 Great Britain Oct. 20, 1954 93,979 Sweden Dec. 28, 193 

1. IN A COMPRESSOR OR SIMILAR DEVICE OF THE TYPE HAVING (A) A HOUSING WITH INTERSECTING CYLINDRICAL ROTOR CHAMBERS AND SUCTION AND DISCHARGE PORTS ARRANGED DIAGONALLY OPPOSITE EACH OTHER NEAR THE ENDS OF SAID HOUSING, AND (B) A PAIR OF COMPLEMENTARY HELICALLY THREADED ROTORS CONSISTING OF A MAIN ROTOR AND A GATE ROTOR EACH HAVING A PLURALITY OF THREADS WITH CREST EDGES AND TROUGHS, (C) SAID ROTORS BEING ROTATABLY SUPPORTED WITHIN THE CHAMBERS OF SAID HOUSING AND COOPERATING WITH EACH OTHER AND THE HOUSING TO FORM POCKETS AS THE SUCTION END OF THE ROTORS FOR RECEIVING FLUID THROUGH SAID SUCTION PORT, TO ADVANCE SAID POCKETS AND THE FLUID THEREIN AXIALLY ALONG THE ROTORS AND TO EXHAUST THE FLUID AT THE DISCHARGE END OF THE ROTORS THROUGH THE THE DISCHARGE PORT AS THE ROTORS REVOLVE ABOUT THE AXES THEREOF, (D) THE THREADS OF EACH ROTOR HAVING SEALING ENGAGEMENT WITH THE TROUGHS OF THE MATING ROTOR THROUGHOUT THE LENGTHS OF THE ROTORS, AND ALSO HAVING SEALING ENGAGEMENT WITH THE HOUSING THROUGHOUT AT LEAST THOSE PORTIONS OF THE LENGTHS OF THE THREADS WHICH EXTEND BETWEEN THE SUCTION PORT AND THE DISCHARGE PORT, AND (E) THE THREADS OF THE MAIN ROTOR LYING SUBSTANTIALLY OUTSIDE THE PITCH CIRCLE THEREOF AND THE THREADS OF THE GATE ROTOR LYING SUBSTANTIALLY INSIDE THE PITCH CIRCLE THEREOF; THE IMPROVEMENT WHICH COMPRISES: (1) EACH OF SAID ROTORS HAVING AXIALLY EXTENDING COMPRESSION AND DISCHARGE AREAS WHEREIN THE ROTOR THREADS ARE OF DIFFERENT SHAPES, THE COMPRESSION AREAS EXTENDING FROM THE SUCTION ENDS OF THE ROTORS TO THE LEADING EDGE OF THE DISCHARGE PORT AND THE DISCHARGE AREAS EXTENDING FROM SAID EDGE TO THE DISCHARGE ENDS OF THE ROTORS, (2) THE THREADS OF THE MAIN ROTOR HAVING LANDS AT THE TIPS THEREOF OF SUBSTANTIALLY UNIFORM WIDTH AND BEING OF GENERATED FORM SUBSTANTIALLY FROM TIP TO ROOT THEREOF THROUGHOUT THE AXIAL LENGTH OF THE COMPRESSION AREA AND HAVING ARCUATE TIPS IN THE DISCHARGE AREA WHICH GRADUALLY INCREASE IN ARCUATE WIDTH TOWARD THE DISCHARGE END OF THE ROTOR, THE FLANKS OF THE THREADS IN THE DISCHARGE AREA BETWEEN THE ARCUATE TIPS AND THE ROOTS THEREOF BEING OF GENERATED FORM, THE GENERATED PORTIONS OF THE MAIN ROTOR THREADS BEING GENERATED BY THE CREST EDGES OF THE GATE ROTOR THREADS AND THE ARCUATE TIPS OF THE MAIN ROTOR THREADS HAVING THEIR CENTERS OF CURVATURE SUBSTANTIALLY ON THE PITCH CIRCLE OF SAID THREADS MIDWAY BETWEEN THE SIDES OF THE THREADS, AND (3) THE THREADS OF THE GATE ROTOR BEING COMPLEMENTARY TO THOSE OF THE MAIN ROTOR, (4) WHEREBY THE THREADS OF THE MAIN AND GATE ROTORS COOPERATE TO FORM AN UNBROKEN SEAL THROUGHOUT THE COMPRESSION AREAS, FORM PROPER SEALS THROUGH THE DISCHARGE AREA, AND DO NOT FORM CLOSED POCKETS AT THE DISCHARGE ENDS OF THE ROTORS. 